The research presents a functional perspective of the structure of the aortic valve of the heart. Investigation of the surface and internal structure of valve parts is carried out with a view to how they bear the stresses of constant opening and closing of the valve. Examination of the ultrastructure of valve leaflets and attachments includes a study of their fibrous and cellular compositions, Special interest currently focuses on unusual fibroblasts in valve leaflets. Turnover in valve tissues is studied by radioautography as a means of understanding the maintenance of the normal valve under stress. Experimental models of bicuspid and other abnormal aortic valves are being developed for structural and tissue turnover studies. Pathological alterations in these valves are under investigation. Similar changes that occur in bioprosthetic valves implanted in experimental animals are also being studied histologically and ultrastructurally.